Evaluation of Mid-Plane Packaging for Telecommunication Systems

Transcription

1 Evaluation of Mid-Plane Packaging for Telecommunication Systems Nobuaki Sugiura* and Katsumi Kaizu** * NTT Network Service Systems Laboratories Transport Network Systems Laboratory , Midori-cho, Musasino-shi, Tokyo , Japan Phone: Fax: / Sugiura.Nobuaki@nslab.ntt.co.jp **Sanwa Denki Kogyo Co., Ltd , Nakano, Nakano-ku, Tokyo , Japan Abstract A mid-plane packaging that is suitable for multi interface implementation was developed in this work. It separates the common function blocks and incidental function blocks into separate blocks. This packaging design reduces the number of signal layers for redundant signal-path in a backplane, thus, the connection reliability is greatly improved. This paper illustrates a general idea of the mid-plane packaging and provides fundamental technical issues, such as cooling performance, signal transmission capability for a through-type connector, and a cable support structure for applying this packaging to the telecommunication systems. Key words: Mid-plane Packaging, Multi Interface Implementation, Redundant Connection, and Electronic Packaging. 1. Introduction Telecommunication systems operating on B-ISDNs require high-throughput and multiple interfaces for computer, voice, video, data, and broadcast connections. The authors previously developed small planar packaging (SPP) 1,2 for high-throughput switching applications. For systems accommodating many kinds of interfaces and redundant signal-path connections, the researchers have conducted investigation using function blocks for interface implementation, that is, common blocks and incidental blocks. Using this approach, a mid-plane packaging configuration for telecommunication systems has been developed. Recently, the focus of this packaging type is for standardization 9 from the viewpoint of interface implementation. In this paper, the benefits of using multiple interfaces and redundant connections in this mid-plane packaging are described. In addition, a comparison with conventional rack-type packaging and evaluation results of cooling and signal transmission capability is also conducted. 2. Mid-Plane Packaging Outline As shown in Figure 1, the backplane normally attached to the backside of a rack in conventional rack-type packaging is set in the middle of this rack. One can refer to it by a backplane a midplane. Plug-in units can be connected to the mid-plane from both the front and back sides of the mid-plane. This packaging configuration uses through-type connectors as shown in Figure 2. connection is performed on the face plate of the backside plug-in units. This system applies 1.27-mm staggered grid through-type connectors. 16

2 Evaluation of Mid-Plane Packaging for Telecommunication Systems Through-type connector and package connector Plug-in unit (back side) Figure 1. Diagram of mid-plane packaging. Mid-plane Rack Plug-in unit (front si Telecommunication systems require redundant connections to maintain signal path reliability. One can estimate the signalpath implementation and the number of layers in the backplane 3. Features of Mid-Plane Packaging (or the mid-plane) based on the switching block model shown in Figure 4. Each signal path is terminated at a line interface block and has redundant connections with the switching and interface 3.1. Multi Interface Implementation 9 blocks. The redundant connections estimated using this function block configuration model are shown in Figure 5. The fol- Many kinds of interfaces, ATM (Asynchronous transfer mode), SDH (Synchronous Digital Hierarchy), Fiber channel, and HIC lowing assumptions were adopted in this work; (Heterogeneous Interconnect), might be connected to telecommunication systems in a multi-media network. When conven- the transmission interface enables parallel transmission of the clock, frame, and data signals; tional rack-type packaging is used to accommodate these interfaces, the interface function blocks are packaged in plug-in units, the number of data paths is determined by the link speed and the physical speed of data transmission; as shown in Figure 3. Since common and incidental if the physical speed is more than 100 Mbit/s, then a differential transmission is applied for these signals; and are mounted on the same board, a board must be designed for each interface function even if the common a clock is supplied to each function block, and a 64-bits are the same. If one would mount each function block separately control-signal bus is connected to each block. in a conventional rack-type packaging, the separated function- Therefore, the number of the signal transmission interface is block plug-in units would have to be mounted side by side, making the rack width large. In this proposed packaging, the function blocks are mounted separately so as not to enlarge the rack width size significantly. To use this packaging approach, it was necessary to define connection interfaces between the front and back-side plug-in units. Achieving this design scheme, the following issues need to be considered; the phase conditions of clock, data, and frame, the electrical level and transmission speed, and the pin assignment. With this packaging design, even if a signal transmission interface is changed, a plug-in unit for the incidental needs to be designed, and this unit can be easily changed according to specific interface mentioned above. Interface B plug-in unit Backplane Connector housing Common Incidental Common Incidental Interface A plug-in unit Press-in pin 1.27-mm staggered grid Figure 3. Interface function mounting using plug-in units in conventional rack-type packaging. Mid-plane Figure mm staggered grid through-type connectors Redundant Implementation For Signal Connection Path 4 17

3 (one clock + one frame + data). The number of data is determined by (link speed / physical speed). In case of the conventional rack-type packaging, the redundant and the self-connection is required in the backplane, so the number of signal transmission interface becomes two times of (one clock + one frame + data). On the other hand, the self-connection is done with the through-type connector for the mid-plane packaging, so the number of signal transmission interface is reduced compared to the conventional rack-type packaging. In the following section, technical issues for applying this packaging to telecommunication systems will be discussed. C Line interface Line interface Control-signal bus Control-signal bus Figure 4. Evaluated switching block. 3 2 Conventional rack-type packaging Mid-plane packaging Switch and interface Switch and interface 4. Structural Study Points 4.1. Signal Transmission Capability of The Through-Type Connector The front and back-side plug-in units are connected to the mid-plane by using through-type connectors consisting of pressin pins (Figure 2). Since the pins sometimes have wire wrapping, the pin length of the back-side is a little longer (about 6 mm) than that of the front-side. The authors have measured the effect of this longer length on signal transmission and confirmed 156 Mbit/s single-ended transmission with a signal to ground pin assignment ratio of between 1-to-1 and 1-to-1.5, Reference 5. The signal transmission capability using an ATM/SDH interface converter (Figure 6) has been measured. A test signal has been generated at some fixed transmission speed and this signal is transmitted from the transmission block to the receive block through the through-type connector. At the same time, four simultaneous noise signals are implemented in the connector neighboring of the signal pin under 1-to-1 signal-to-ground pin assignment ratios, and run through inverse direction against the signal direction. The transmitted signal is measured to determine whether it has been received correctly or not, and confirmed 156 Mbit/s signal transmission. The I/O, the ATM/SDH converter, and the driver and the receiver have performance of more than 600 Mbit/s, therefore, one can assume that the noise induced in the connector limits the signal transmission capability. The signal transmission capability using a simplified connector model 6 and considering the switching noise and crosstalk has been evaluated. The electrical parameters are calculated using following equations, L = µ 0 l pin (ln(2l pin /a) )/2π (1) C = K 1 (l pin - l hou )/l pin + K 1 ε r l hou /l pin (2) Physical speed of data signal (Mb/s) Figure 5. Calculated number of signal layers. L m = µ 0 (l coup ln(((l coup 2 + d 2 ) + l coup ) 1/2 / d) - (l coup 2 + d 2 ) 1/2 + d) / 2π (3) C m = K 2 (l coup - l hou )/l coup + K 1 ε r l hou /l coup (4) K 1 = 4π ε 0 l pin / ln(((1/2 2 + a 2 ) 1/ ) / a) (5) K 2 = 4π ε 0 l coup / ln((d - a)/a) (6) 18

4 Evaluation of Mid-Plane Packaging for Telecommunication Systems Through-type connectors Front-side plug-in unit Back-side plug-in unit ATM Analyser O/E Signal termination I/O I/O ATM/SDH converter Driver 10 Signal O/E I/O I/O SDH/ATM termination Receiver converter 156-Mb/s ATM signal 156-MHz clock Figure 6. Function block configuration of ATM/SDH interface converter evaluation unit using mid-plane packaging. Where l pin is the connector pin length (m), l coup is the coupled signal pin length (m), l hou is the housing length (m), a is the equivalent pin diameter (m), d is the pin pitch between signal pins (m), µ 0 is the free space magnetic permeability, ε 0 is the free space dielectric constant, and ε r is the relative dielectric constant of the mold. Connector crosstalk is derived using the following equations, V N = 1/2 (Z 0 C m + L m / Z 0 ) V d /t (7) V F = 1/2 (Z 0 C m - L m / Z 0 ) V d / t (8) In this case, Z 0 is the characteristic impedance (ohm), C m is the coupling capacitance (F), L m is the mutual inductance (H), V d is the driving signal amplitude (V), and t is the signal rise time (s), V N is the near end crosstalk (V), and V F is the far end crosstalk (V). The following equation for switching noise (V n ) in the connector is used. In this case, one would assume 25% of the signal pins in the connector are driving. It is important to point out that it is necessary that one would satisfy this noise condition Tr (ns) Signal transmission speed = 1/ (6 x Tr) ` 1 Figure 7. Signal transmission capability evaluation Protection of Electro Magnetic Interference (EMI) Since the cable connections are performed on the face plate of the back-side plug-in units, the face plate was designed to protect against EMI, mainly generated by the connecting cables. A shieldgasket spring and an injector/ejector with a metal contact was used to create a good connection (contact resistance of under 20 mω) between the rack frame and the face plate, shown in Figure 8. The electromagnetic emission noise generated by signal transmission circuits is measured with a three-meter method, and compared the measured noise with or without the face plate. The effect of this face plate was about 2 to 5 db as shown in Figure 9. V n = K N L di/dt (9) Where K is a coefficient constant, L is the connector inductance (H), and N is the number of simultaneous driving signals. Noise margin of the device > Crosstalk + Switching noise (10) The switching time is assumed to be equal to the signal rise time (T r ), and the noise is thus evaluated. The signal cycle time is assumed to be six times of the signal rise time (T r ). This evaluation results, as shown in Figure 7, showed that about 140 Mbit/s transmission is the maximum speed with single-ended transmission 3. The difference in the speed is due to the difference in the number of simultaneously driven signals. The signal transmission capability can be extended by providing the following criteria, reducing the noise in each connector to match the characteristic impedance between the connector and the signal path (reduce the length of connector pins), and by applying differential transmission. Figure 8. BBack-side plug-in with face plate. 19

5 With face plate Without face plate 80 cm Fan unit area Conventional rack-type packaging area 60 cm Figure 9. Noise reduction with face plate Frequency (MHz) Mid-plane packaging area Fan unit area Conventional rack-type packaging area 4.3. Cooling Capability Pedestal The subracks use conventional rack-type packaging, the midplane packaging can be mounted in a cabinet. However, mixing conventional and mid-plane rack mounting affects the air flow used for cooling. It is concerned about heat accumulation in the front area of the back-side plug-in units of the mid-plane packaging rack due to the depth differences between the mid-plane packaging and the conventional rack type packaging. The authors have thus simulated the cooling capability of this configuration as follows 7. The air flow path was approximated as a rectangular path and the air flow resistance of each path was calculated. Next, the total airflow resistance of a cabinet with a mixed rack-mount configuration was calculated. The airflow was calculated, assuming that the airflow was laminated and the pressure was determined by (airflow) 2. Next, the temperature increase generated by a plug-in unit was calculated. The specifications of the plug-in units are as follows, The conventional rack-type packaging is 330 mm deep and 300 mm high, The mid-plane packaging is 220 mm deep on the frontside, 120 mm deep on the back-side, and 300 mm high, Each rack mounts 38 plug-in units with a mm mounting pitch, Each plug-in unit is 6 mm high, and Each printed board is 1.6 mm thick; the backplane and mid-plane are 2.4 mm thick. The subrack mounting in a cabinet is as shown in Figure 10. The two subracks at the bottom are for conventional racktype packaging, and those at the top are for conventional racktype packaging and mid-plane packaging. Front view Figure 10. Subrack mounting. Side view (cross sect Two cooling fan units are mounted in the cabinets; each unit has eight fans. Each fan produces a pressure of 140 Pa (Max) and moves 6.4 m 3 of air per minutes (Max). The two upper subracks are cooled by push-pull fans, and the two bottom subracks are cooled by pull-type fans. The temperature increase between a conventional rack and this mid-plane rack for 20, 30, and 40 watts per plug-in unit has been compared. The heat amount of the plug-in unit for the midplane is sum of heat of the front-side and the back-side plug-in unit per slot. These calculation results are close to the measurement results as shown in Table 1. The temperature rise of the top subrack has been measured, as shown in Figure 10. This result shows that about 40W power consumer per plug-in unit is available. The cooling capability is simulated using 3-dimensional heat analysis and found almost the same cooling ability 8. Table 1. Temperature increase. Power consumption of plug- Power consumption plug- Power consumption consumption in units units in a Mid-plane in a Mid-plane Temperature increase(s) increase ( ) of plug-in plug-in units units rack (W) (W) in a conventional a conventional rack (W) Front Sideside Back Side side Calculated Measured rack (W) S O R O Q P Q V P R P W. W P V Q O P O P S. O P Q P S V X. T X Support Since the cable connection is performed on the face plate of the back-side plug-in unit, the researchers designed a cable support to fix the cables so they do not interfere insertion and extrac-

6 Evaluation of Mid-Plane Packaging for Telecommunication Systems tion of plug-in units. It swings down 90 degrees to give ample room for operation (Figure 11). When the cable support is down, it is supported as a one-end holding condition. The researchers have calculated the mechanical strength considering the bending moment and retention force in order to design the cross section structure and material. The load distribution model used is illustrated in Figure 12. support Back-side 5. Conclusion The mid-plane packaging design and implementation was demonstrated and explained the technical issues for applying this packaging to the telecommunication systems. This packaging is suitable for the multi-interface implementation separating the common function block and the incidental block with the unified interface and is useful to reduce the number of the signal layers for redundant signal path implementation in the backplane. The authors also developed the cable support that does not disturb plug-in unit operation. This packaging is going to be introduced to the future ATM telecommunication system. References Figure 11. support configuration. Bracket support (side) holder Optical fiber Lock fixture -mounting panelelectrical cable Lock fixture 2.57 N -mounting panel N/cm Electric cable 1.19 N/cm holder 6.02 N Optical fiber 0.28 N/cmBracket 0.41 N/cm haching Concentrated force Distributed force Figure 12. Load distribution model. Cabin suppo support 0.51 N/cm 1. T. Kishimoto, K. Yasuda, H. Oka, Y. Kaneko, and M. Kawauchi, Small Planar Packaging System For Highthroughput ATM Switching Systems, Electron Letters, Vol. 31, No. 7, pp , K. Yasuda, T. Kishimoto, K. Kaizu, Y. Kaneko, M. Kawauchi, and H. Oka, Small Planar Packaging System Combined with Card on Board Packaging For High-Speed, High-Density Switching Systems, Proceedings of the 1995 International Symposium of Microelectronics, ISHM 95, pp , N. Sugiura, M. Nakamura, and K. Okazaki, A Study on System Packaging for Multi-Interface Implementation, Proceedings of the 1996 Electronics Society Fall Conference of IEICE, SC-5-10, 1996 (in Japanese). 4. N. Sugiura, M. Nakamura, K. Kaizu, and T. Kishimoto, Telecom System Packaging for Line Protection and Multi- Interface Implementation, Proceedings of the IEPC, pp , M. Nakamura, N. Sugiura, K. Kaizu, and K. Yasuda, Evaluation for Signal Transmission Capability of Interconnection Between Packages Using Through-Type Connector, Technical Report of IEICE, EMD95-56, pp , 1996 (in Japanese). 6. N. Sugiura and K. Yasuda, A High-Density Multi pin Connector for High-Speed Signal Transmission in a Rack System, Proceedings of the 41st Electronic Components and Technology Conference, ECTC 91, pp , D. S. Steinberg, Cooling Techniques for Electronic Equipment, John Wiley & Sons, Inc., Y. Shouno, S. Kasuga, and M. Abe, Verification of Thermal Design in a Mid-Plane Packaging System, Technical Report of IEICE, SSE96-167, pp , 1996(in Japanese). 9. IEC : Rear Mounting of Plug-In Units in a Subrack for Subracks and Associated Plug-In Units With Extended Features Added to IEC and IEC , IEC 48D/207/CDV,

7 About the authors Nobuaki Sugiura received the B.E. Degree in Electrical Engineering from Nagoya Institute of Technology, and the M.E. and D.E. Degrees in Electrical Engineering from Nagoya University, Nagoya, Japan, in 1979, 1981, and 1996, respectively. He joined NTT Electrical Communications Laboratories in Since then, he has been mainly engaged in research and evaluation on signal transmitting capability in a rack system and packaging for communication switching systems. He is a Senior Research Engineer in NTT Network Service Systems Laboratories. He is a member of the Institute of Electronics, Information and Communication Engineers of Japan, IEEE, and IMAPS Societies. Katsumi Kaizu received the B.S. Degree in Electronics Engineering from Tokyo Electrical Engineering University, Japan, in He joined the Musashino Electrical Communication Laboratory of Nippon Telegraph and Telephone Corporation in 1973, where he was engaged in reliability studies on LSI and optical semiconductor devices and research on high speed, high density packaging technologies for Broadband ISDN systems. Since 1998, he has been engaged in development of electrical and optical connectors for telecommunication systems at the Sanwa Electric Industry Corporation. Mr. Kaizu is the member of the Institute of Electronics, Information and Communication Engineers of Japan. 22